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71 lines
2.6 KiB
71 lines
2.6 KiB
# This library is free software.
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#
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# It was originally distributed under the terms of the GNU Lesser
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# General Public License Version 2.
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#
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# python-messaging opts to apply the terms of the ordinary GNU
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# General Public License v2, as permitted by section 3 of the LGPL
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# v2.1. This re-licensing allows the entirety of python-messaging to
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# be distributed according to the terms of GPL-2.
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#
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# See the COPYING file included in this archive
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#
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# The docstrings in this module contain epytext markup; API documentation
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# may be created by processing this file with epydoc: http://epydoc.sf.net
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"""Iterator with "value preview" capability."""
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class PreviewIterator(object):
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"""An ``iter`` wrapper class providing a "previewable" iterator.
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This "preview" functionality allows the iterator to return successive
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values from its ``iterable`` object, without actually mvoving forward
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itself. This is very usefuly if the next item(s) in an iterator must
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be used for something, after which the iterator should "undo" those
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read operations, so that they can be read again by another function.
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From the user point of view, this class supersedes the builtin iter()
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function: like iter(), it is called as PreviewIter(iterable).
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"""
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def __init__(self, data):
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self._it = iter(data)
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self._cached_values = []
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self._preview_pos = 0
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def __iter__(self):
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return self
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def next(self):
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self.reset_preview()
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if len(self._cached_values) > 0:
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return self._cached_values.pop(0)
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else:
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return self._it.next()
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def preview(self):
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"""
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Return the next item in the ``iteratable`` object
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But it does not modify the actual iterator (i.e. do not
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intefere with :func:`next`.
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Successive calls to :func:`preview` will return successive values from
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the ``iterable`` object, exactly in the same way :func:`next` does.
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However, :func:`preview` will always return the next item from
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``iterable`` after the item returned by the previous :func:`preview`
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or :func:`next` call, whichever was called the most recently.
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To force the "preview() iterator" to synchronize with the "next()
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iterator" (without calling :func:`next`), use :func:`reset_preview`.
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"""
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if self._preview_pos < len(self._cached_values):
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value = self._cached_values[self._preview_pos]
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else:
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value = self._it.next()
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self._cached_values.append(value)
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self._preview_pos += 1
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return value
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def reset_preview(self):
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self._preview_pos = 0
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